Custom - Too Many

link - learn.microsoft.com/en-us/office/troubleshoot/excel/too-many-different-cell-formats-in-excel 
link - support.microsoft.com/en-gb/topic/unused-styles-are-copied-from-one-workbook-to-another-in-excel-2010-76384fc5-53be-9f88-1cbf-292bd4939db7 
link - support.microsoft.com/en-gb/topic/unused-styles-are-copied-from-one-workbook-to-another-workbook-in-excel-2007-eac665b8-1602-385e-4d6c-d13081b8628d 

DWord - 32 bit
HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Excel\Options\DisableCopyUnusedCustomStyles